Linear differential amplifier

ABSTRACT

A differential amplifier with improved linearity. The amplifier includes a circuit comprised of two emitter-coupled pairs, each pair being formed by two transistors, with connections between corresponding collectors, and constant voltage sources for producing offsets between corresponding bases of the emitter-coupled pairs. The improved linearity is achieved by obtaining outputs as sums of collector currents with offsets. The emitter areas of the transmitters can be of the minimum size available. This feature, when combined with the use of emitter-followers as the constant voltage sources, enable the differential amplifier to achieve a high S/N ratio, a good high-frequency characteristic, a high direct current gain, and a high-speed operation capability along with the improved linearity. In addition, the linearity is further improved by using additional diodes connected to the transistors.

This is a continuation-in-part application of our earlier copending,commonly assigned application Ser. No. 07/253,557 filed Oct. 5, 1988,which is now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a linear differential amplifier whichconstitutes a part of an electric filter or a similar device to beincorporated, for example, in an IC.

2. Description of the Prior Art

Recently, it has become a common practice to incorporate electricfilters comprised of differential amplifiers in an IC. But, adifferential amplifier of the operational amplifier type with doubleamplification stages does not possess a satisfactory frequencycharacteristic in the high-frequency range such as the video frequencyrange. Because of this, an electric filter is often realized byconstructing a gyrator or a biquad filter with a differential amplifierincluding a capacitor as a load, which is regarded as a single stageintegrator. Such a differential amplifier is shown in FIG. 1, where itis comprised of a pair of bipolar transistors 141 and 142 which form anemitter-coupled pair 143, a capacitor 144 connected between collectorsof the transistors 141 and 142 as a load, a constant current source 145connected between the round and emitters of the transistors 141 and 142as a load, a constant current source 145 connected between the groundand emitters of the transistors 141 and 142 for supplying emittercurrents 2I_(e), load resistors or their equivalents 146 and 147connected to the collectors of the transistors 141 and 142, outputterminals 148A and 148B connected to the collectors of the transistors141 and 142, and input terminals 149A and 149B connected to bases of thetransistors 141 and 142. In FIG. 1, V_(cc) stands for the power sourcevoltage.

However, an emitter-coupled pair formed by bipolar transistors like theone shown in FIG. 1 possesses poor linearity and changes itstransconductance depending on the level of input signals. Consequently,an electric filter comprised of a differential amplifier of this typechanges its characteristic depending on the level of input signals, andtherefore is not satisfactory in this respect.

There has been proposed, a differential amplifier with an improvedlinearity, such as the one shown in FIG. 2, which has been disclosed byJ. O. Voorman et al. in "Bipolar integration of analog gyrator andLaguerre type filters" Proc. ECCTD '83, Stuttgart, pp. 108-110. Thisdifferential amplifier is comprised of two emitter-coupled pairs 140 and150 formed by a pair of transistors 151 and 152, and 153 and 154,respectively, where each of the transistors 152 and 153 has an emitterarea four times larger than that of the transistors 151 and 153.Collectors of the transistors 152 and 153 are connected with each otheras well as with a load resistor 146 which converts output current I₃ ofthese two transistors, while collectors of transistors 151 and 154 areconnected with each other as well as with a load resistor 147 whichconverts output currents I₄ of these two transistors. It furtherincludes a constant current source 155 for the emitter-coupled pair 140for supplying emitter current I_(e), and a constant current source 156for the emitter-coupled pair 150 for supplying emitter currents I_(e),output terminals 148A and 149B connected to the collectors of thetransistors 152 and 153, and 151 and 154, respectively, input terminals149A and 149B connected to the bases of the transistors 152 and 153, and151 and 154, respectively. As in FIG. 1, Vcc stands for the power sourcevoltage in FIG. 2.

The improvement in linearity is achieved by producing output currents I₃and I₄ as sums of the collector currents with an offset ratio of 1:4from the transistors of the emitter-coupled pairs 140 and 150, theoffset being caused by the fact that these emitter-coupled pairs 140 and150 comprise transistors with an emitter area ratio of 1:4.

FIG. 3 shows the input-output characteristic of this differentialamplifier contrasted with that of the conventional one. In FIG. 3 curveA is the characteristic curve of the differential amplifier of FIG. 2while curve B is the characteristic curve of the differential amplifierof FIG. 1, and R_(L) is the resistance of the load. By comparing thesetwo characteristic curves, it can be seen that the range of input levelswith the output distortion up to 1% has been increased from ±17 mVpp forthe differential amplifier of FIG. 1 to ±48 mVpp for that of FIG. 2.

By constructing a gyrator or a biquad filter with such a differentialamplifier of the improved linearity, an improvement can be made in afrequency characteristic by regarding the differential amplifier as asingle stage integrator, but obtaining a high direct current gainbecomes difficult. The lowering of direct current gain in the integratorof an electric filter causes lowering of the quality Q of the devicethat includes the electric filter, as can be seen from a comparison to apassive filter comprised of an LC circuit.

To cope with this difficulty, a differential amplifier with its outputterminals connected, not directly to bases of another differentialamplifier but through emitter-followers to bases of another differentialamplifier so as to prevent the lowering of direct current gain has beenproposed by K. W. Moulding et al. in "Gyrator Video Filter IC withAutomatic Tuning" IEEE Journal of Solid State Circuits, Vol. SC-15, No.6, pp. 963-968, Dec. 1980.

But, connecting the differential amplifier of FIG. 2 to anemitter-follower is equivalent to connecting a transistor with anemitter area five times larger than the minimal emitter area available.Since the base-emitter capacitance of a transistor is proportional tothe emitter area, when the emitter area is five times larger as in thiscase, the base-emitter capacitance also becomes five times greater.Here, it is not possible to reduce the base-emitter capacitance byreducing the base-emitter capacitance of the transistor of a connectingdifferential amplifier because a base-emitter capacitance of atransistor, which typically is 1 pF-5 pF, is determined by the smallestsize manufacturable which is dictated by the manufacturing process.Thus, in this case the increase in the base-emitter capacitance isunavoidable.

Also, in general, it is ideal for an integrator to possess a pole at avery low frequency and no other poles or zeros at any other frequencies.But, since an actual integrator possesses a number of poles and zerosdue to the limited quality of transistors incorporated, it is necessaryin order to produce a good electric filter that these poles and zerosare at frequencies 50 to 100 times that of the cutoff frequency of thefilter. This means if an electric filter were to have a cutoff frequencyof 10 MHz, a second pole or zero have to be at 500 MHz to 1 GHz. Inother words, it is necessary to take into consideration frequencies muchhigher than those used in order to produce a good electric filter.

Now, the aforementioned differential amplifier with its output terminalsconnected to emitter-followers can be considered as a low-pass filtershown in FIG. 4(A) or its equivalent circuit shown in FIG. 4(B) formedby a base-emitter capacitance C_(be) and output resistance r_(o) and abase resistance r_(b) of the emitter-follower 157. In FIG. 4, V_(cc) isthe power source voltage, V_(in) is an input voltage, and V_(out) is anoutput voltage.

In this configuration, there is a pole at the frequency ##EQU1## and ifthe differential amplifier of FIG. 1 was used with a collector currentfor the emitter-followers 57 of 0.5 mA, a base-emitter capacitanceC_(be) of 2 pF, and a base resistance r_(b) of 100 Ω; then since

    r.sub.o =1/g.sub.m =52Ω                              (2)

the pole frequency is ##EQU2## On the other hand, if a differentialamplifier of FIG. 2 was used with a collector current for theemitter-follower 57 of 1 mA and a base resistance r_(b) of 40 Ω, thensince

    C.sub.be =2 pF×5=10 pF

    r.sub.o =1/g.sub.m =26Ω                              (4)

the pole frequency is ##EQU3##

which is less than a half of the previous case, and for the reasonexplained above, this implies a considerably inferior frequencycharacteristic.

The preceding arguments show that constructing an emitter-coupled pairby transistors with an emitter area ratio of 1:4 necessitates the use ofa transistor with an emitter area four times larger than the minimumsize available and this causes the increase in the base-emittercapacitance C_(be) which deteriorates the frequency characteristic atthe high frequency range.

In addition, it is necessary to drive a differential amplifier with apower source with very low impedance in order to operate it at ahigh-speed. This is quite disadvantageous because this means that if thebase-emitter capacitance C_(be) in the last example was 5 pF and thepole frequency f_(p) was to be at 500 MHz, then the collector current ofthe emitter-follower 157 would have to be 4 mA, so that not only thepower consumption increases considerably, but also the base current ofthe emitter-follower 157 becomes prohibitive.

Furthermore, since the increase in an emitter area causes the loweringof a cutoff frequency, such an amplifier is not suitable for any devicethat requires a highspeed operation.

On the other hand, in a device requiring a high S/N ratio, the size ofthe transistor is increased in order to reduce base resistance. Now,with a differential amplifier with transistors having an emitter arearatio as much as 1:4, the noise level is determined by the baseresistance of the transistor with the smaller emitter area which in thiscase has the higher base resistance. But considering the requiredfrequency characteristic and the designed device size, the highlyrestricted limit on the allowable increase in the size of a transistormakes this type of a differential amplifier unfavourable even in thisrespect regarding the noise unless the increase in the manufacturingcost were to be overlooked.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide adifferential amplifier capable of achieving an improved linearity, agood high-frequency characteristic, a good S/N ratio, a high directcurrent gain, and a high-speed operation, all at once.

According to one aspect of the present invention there is provided alinear differential amplifier, comprising: a pair of first and secondtransistors with their emitters coupled to each other; a pair of thirdand fourth transistors with their emitters coupled to each other, acollector of said first transistor being connected to a collector ofsaid third transistor and a collector of said second transistor beingconnected to a collector of said fourth transistor; a pair of inputterminals, one of which being coupled to a base of said firsttransistor, the other one of which being coupled to a base of saidfourth transistor; a pair of output terminals, one of which beingconnected to said collectors of said first and said third transistor,the other one of which being connected to said collectors of said secondand said fourth transistors; first voltage source means for applyingfirst offset DC voltage between one of said input terminals and a baseof said third transistor, said first voltage source means including afirst pair of emitter-followers with each said emitter-followerincluding transistors of same emitter areas but different collectorcurrents, and first emitter current sources for each transistor of saidfirst pair of emitter-followers which supply emitter currentscorresponding to the collector currents; second voltage source means forapplying second offset DC voltage of the same magnitude as said firstoffset DC voltage, between one of said input terminals and a base ofsaid second transistor, said second voltage source means including asecond pair of emitter-followers with each said emitter-followerincluding transistors of same emitter areas but different collectorcurrents, and second emitter current sources for each transistor of saidsecond pair of emitter-followers which supply emitter currentscorresponding to the collector currents; constant current source meansfor supplying emitter currents to said first, second, third, and fourthtransistors; and load resistor means for converting collector currentsof said first, second, third, and fourth transistors into outputvoltages.

According to another aspect of the present invention there is provided alinear differential amplifier, comprising: a pair of first and secondtransistors with their emitters coupled to each other; a pair of thirdand fourth transistors with their emitters coupled to each other, acollector of said first transistor being connected to a collector ofsaid third transistor and a collector of said second transistor beingconnected to a collector of said fourth transistor, and said first andfourth transistors having emitter areas different from those of saidsecond and third transistors; a pair of input terminals, one of whichbeing coupled to a base of said first transistor, the other one of whichbeing coupled to a base of said fourth transistor; a pair of outputterminals, one of which being connected to said collectors of said firstand said third transistor, the other one of which being connected tosaid collectors of said second and said fourth transistors; firstvoltage source means for applying first offset DC voltage between one ofsaid input terminals and a base of said third transistor, said firstvoltage source means including a first pair of emitter-followers witheach said emitter-follower including transistors of different emitterareas, and first emitter current sources for supplying constant emittercurrents to said transistors of said first pair of emitter followers;second voltage source means for applying second offset DC voltage of thesame magnitude as said first offset DC voltage, between one of saidinput terminals and a base of said second transistor, said secondvoltage source means including a second pair of emitter-followers witheach said emitter-follower including transistors of different emitterareas, and second emitter current sources for supplying constant emittercurrents to said transistors of said second pair of emitter followers;constant current source means for supplying emitter currents to saidfirst, second, third, and fourth transistors; and load resistor meansfor converting collector currents of said first, second, third, andfourth transistors into output voltages.

According to another aspect of the present invention there is provided alinear differential amplifier, comprising: a pair of first and secondtransistors with their emitters coupled to each other; a pair of thirdand fourth transistors with their emitters coupled to each other, acollector of said first transistor being connected to a collector ofsaid third transistor and a collector of said second transistor beingconnected to a collector of said fourth transistor, and said first andfourth transistors having emitter areas different from those of saidsecond and third transistors; a pair of input terminals, one of whichbeing coupled to a base of said first transistor, the other one of whichbeing coupled to a base of said fourth transistor; a pair of outputterminals, one of which being connected to said collectors of said firstand third transistor, the other one of which being connected to saidcollectors of said second and said fourth transistors; first voltagesource means for applying first offset DC voltage between one of saidinput terminals and a base of said third transistor, said first voltagesource means including a first pair of emitter-followers with each saidemitter-follower including transistors of same emitter areas butdifferent collector currents, and first emitter current sources for eachtransistor of said first pair of emitter-followers which supply emittercurrents corresponding to the collector currents; second voltage sourcemeans for applying second offset DC voltage of the same magnitude assaid first offset DC voltage, between one of said input terminals and abase of said second transistor, said second voltage source meansincluding a second pair of emitter-followers with each saidemitter-follower including transistors of same emitter areas butdifferent collector currents, and second emitter current sources foreach transistor of said second pair of emitter-followers which supplyemitter currents corresponding to the collector currents; constantcurrent source means for supplying emitter currents to said first,second, third, and fourth transistors; and load resistor means forconverting collector currents of said first, second, third, and fourthtransistors into output voltages.

According to another aspect of the present invention, there is provideda linear differential amplifier, comprising: a pair of first and secondtransistors with their emitters coupled to each other, each of whichhaving a diode connected to its emitter; a pair of third and fourthtransistors with their emitters coupled to each other, each of whichhaving a diode connected to its emitter, a collector of said firsttransistor being connected to a collector of said third transistor and acollector of said second transistor being connected to a collector ofsaid fourth transistor; a pair of output terminals, one of which beingconnected to said collectors of said first and said third transistor,the other one of which being connected to said collectors of said secondand said fourth transistors; a first voltage source means for applyingfirst offset DC voltage between one of said input terminals and a baseof said third transistor, said first voltage source means including afirst pair of emitter-followers with each said emitter-followerincluding transistors of different emitter areas, and first emittercurrent sources for supplying constant emitter currents to saidtransistors of said first pair of emitter-followers; a second voltagesource means for applying second offset DC voltage of the same magnitudeas said first offset DC voltage, between the other one of said inputterminals and a base of said second transistor, said second voltagesource means including a second pair of emitter-followers with each ofsaid emitter-followers including transistors of different emitter areas,and second emitter current sources for supplying constant emittercurrents to the transistors of said second pair of emitter-followers;constant current source means for supplying emitter currents to saidfirst, second, third, and fourth transistors; and load resistor meansfor converting collector currents of said first, second, third, andfourth transistors into output voltages.

According to another aspect of the present invention there is provided alinear differential amplifier, comprising: a pair of first and secondtransistors with their emitters coupled to each other, each of whichhaving a diode connected to its emitter; a pair of third and fourthtransistors with their emitters coupled to each other, each of whichhaving a diode connected to its emitter, a collector of said firsttransistor being connected to a collector of said third transistor and acollector of said second transistor being connected to a collector ofsaid fourth transistor; a pair of output terminals, one of which beingconnected to said collectors of said first and said third transistor,the other one of which being connected to said collectors of said secondand said fourth transistors; a first voltage source means for applyingfirst offset DC voltage between one of said input terminals and a baseof said third transistor, said first voltage source means including afirst pair of emitter-followers with each said emitter-followerincluding transistors of different emitter areas and different collectorcurrents, and emitter current sources for each transistor of theemitter-followers which supply emitter currents corresponding to thecollector currents; a second voltage source means for applying secondoffset DC voltage of the same magnitude as said first offset DC voltage,between the other one of said input terminals and a base of said secondtransistor, said second voltage source means including a second pair ofemitter-followers with each of said emitter-followers includingtransistors of different emitter areas and different collector currents,and emitter current sources for each transistor of the emitter-followerswhich supply emitter currents corresponding to the collector currents;constant current source means for supplying emitter currents to saidfirst, second, third, and fourth transistors; and load resistor meansfor converting collector currents of said first, second, third, andfourth transistors into output voltages.

According to another aspect of the present invention there is provided alinear differential amplifier, comprising: a pair of first and secondtransistors with their emitters coupled to each other, one of whichhaving a number of diodes connected to its emitter while another one ofwhich having a different number of diodes connected to its emitter; apair of third and fourth transistors with their emitters coupled to eachother, one of which having a number of diodes connected to its emitterwhile another one of which having a different number of diodes connectedto its emitter, a collector of said first transistor being connected toa collector of said third transistor and a collector of said secondtransistor being connected to a collector of said fourth transistor, andsaid first and fourth transistors having emitter areas different fromthat of said second and third transistors; a pair of input terminals,one of which being coupled to the base of said first transistor, theother one of which being coupled to the base of said fourth transistor;a pair of output terminals, one of which being connected to thecollectors of said first and said third transistor, the other one ofwhich being connected to the collectors of said second and said fourthtransistors; first voltage source means for applying first offset DCvoltage between one of said input terminals and a base of said thirdtransistor, said first voltage source means including a first pair ofemitter-followers with each of said emitter-followers includingtransistors of different emitter areas, and first emitter currentsources for supplying constant emitter current to said transistors ofsaid first pair of emitter-followers; second voltage source means forapplying second offset DC voltage of the same magnitude as said firstoffset DC voltage, between the other one of said input terminals and abase of said second transistor, said second voltage source meansincluding a second pair of emitter-followers with each of saidemitter-followers including transistors of different emitter areas, andsecond emitter current sources for supplying constant emitter currentsto the transistors of said second pair of emitter-followers; constantcurrent source means for supplying emitter currents to said first,second, third, and fourth transistors; and load resistor means forconverting collector currents of said first, second, third, and fourthtransistors into output voltages.

According to another aspect of the present invention there is provided alinear differential amplifier, comprising: a pair of first and secondtransistors with their emitters coupled to each other, one of whichhaving a number of diodes connected to its emitter while another one ofwhich having a different number of diodes connected to its emitter; apair of third and fourth transistors with their emitters coupled to eachother, one of which having a number of diodes connected to its emitterwhile another one of which having a different number of diodes connectedto its emitter, a collector of said first transistor being connected toa collector of said third transistor and a collector of said secondtransistor being connected to a collector of said fourth transistor, andsaid first and said fourth transistors having emitter areas differentfrom that of said second and said third transistors; a pair of inputterminals, one of which being coupled to the base of said firsttransistor, the other one of which being coupled to the base of saidfourth transistor; a pair of output terminals one of which beingconnected to the collectors of said first and said third transistors,the other one of which being connected to the collectors of said secondand said fourth transistors; first voltage source means for applyingfirst offset DC voltage between one of said input terminals and the baseof said third transistor, said first voltage source means including afirst pair of emitter-followers with each of said emitter-followersincluding transistors of the same emitter areas but different collectorcurrents, and first emitter current sources for each of said transistorsof said first pair of emitter-followers which supply emitter currentscorresponding to the collector currents; second voltage source means forapplying second offset DC voltage of the same magnitude as said firstoffset DC voltage, between the other one of said input terminals and thebase of said second transistor, said second voltage source meansincluding a second pair of emitter-followers with each of saidemitter-followers including transistors of the same emitter areas butdifferent collector currents, and second emitter current sources foreach transistor of said second pair of emitter-followers which supplyemitter currents corresponding to the collector currents; constantcurrent source means for supplying emitter currents to said first,second, third, and fourth transistors, and load resistor means forconverting collector currents of said first, second, third, and fourthtransistors into output voltages.

The other features and advantages of the present invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a differential amplifier according to oneexample of the prior art.

FIG. 2 is a circuit diagram of a differential amplifier according toanother example of the prior art.

FIG. 3 is a graph showing the input-output characteristics of the twoprior art differential amplifiers of FIG. 1 and FIG. 2.

FIG. 4(A) and (B) are circuit diagram for explaining the problem of aprior art differential amplifier.

FIG. 5 is a circuit diagram of the first embodiment of a lineardifferential amplifier according to the present invention.

FIG. 6 is a circuit diagram of the second embodiment of a lineardifferential amplifier according to the present invention.

FIG. 7 is a circuit diagram of the third embodiment of a lineardifferential amplifier according to the present invention.

FIG. 8 is a circuit diagram of the fourth embodiment of a lineardifferential amplifier according to the present invention.

FIG. 9 is a circuit diagram of the fifth embodiment of a lineardifferential amplifier according to the present invention.

FIG. 10 is a circuit diagram of the sixth embodiment of a lineardifferential amplifier according to the present invention.

FIG. 11 is a circuit diagram of the seventh embodiment of a lineardifferential amplifier according to the present invention.

FIG. 12 is a circuit diagram of the eighth embodiment of a lineardifferential amplifier according to the present invention.

FIG. 13 is a circuit diagram of the ninth embodiment of a lineardifferential amplifier according to the present invention.

FIG. 14 is a circuit diagram of the tenth embodiment of a lineardifferential amplifier according to the present invention.

FIG. 15 is a circuit diagram of the eleventh embodiment of a lineardifferential amplifier according to the present invention.

FIG. 16 is a circuit diagram of the twelfth embodiment of a lineardifferential amplifier according to the present invention.

FIG. 17 is a circuit diagram of the thirteenth embodiment of a lineardifferential amplifier according to the present invention.

FIG. 18 is a circuit diagram of the fourteenth embodiment of a lineardifferential amplifier according to the present invention.

FIG. 19 is a circuit diagram of the fifteenth embodiment of a linerdifferential amplifier according to the present invention.

FIG. 20 is a circuit diagram of the sixteenth embodiment of a lineardifferential amplifier according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 5, there is shown a first embodiment of a lineardifferential amplifier according to the present invention.

In this embodiment, a linear differential amplifier comprises a firstemitter-coupled pair 10 formed by two transistors Q₁ and Q₂, a secondemitter-coupled pair 20 formed by two transistors Q₃ and Q₄, where acollector 11 of the transistor Q₁ is connected to a collector 13 of thetransistor Q₃ and a collector 12 of the transistor Q₂ is connected to acollector 14 of the transistor Q₄, a first constant voltage source E₁for applying a constant voltage between a base 1 of the transistor Q₁and a base 3 of the transistor Q₃, a second constant voltage source E₂for applying the same voltage applied by the first constant voltagesource E₁ between a base 2 of the transistor Q₂ and a base 4 of thetransistor Q₄, a first load resistor 5 for converting collector currentsof the transistors Q₁ and Q₃ shown collectively as an output current I₁into an output voltage, a second load resistor 6 for convertingcollector currents of the transistors Q₂ and Q₄ shown collectively as anoutput current I₂ into an output voltage, a first constant currentsource 7 for supplying emitter currents I_(e) to the transistors Q₁ andQ₃, a second constant current source 8 for supplying the same emittercurrents I_(e) to the transistors Q₂ and Q₄, output terminals 15 and 16,and input terminals 17 and 18. A base 1 of the transistor Q₁ and a base3 of the transistor Q₃ are connected to an input terminal 17, a base 2of the transistor Q₂ and a base 4 of the transistor Q₄ are connected toan input terminal 18, and the amplifier is emitter-grounded as shown. InFIG. 5, V_(cc) stands for the power source voltage.

In this linear differential amplifier, due to the constant voltagesapplied by the constant voltage sources E₁ and E₂, collector currents ofthe transistors Q₁, Q₂, Q₃, and Q₄ acquire offsets. These collectorcurrents with offsets are then added to yield the output currents I₁ andI₂, which are subsequently converted into output voltages by the loadresistors 5 and 6.

The improved linearity is achieved in this linear differentialamplifier, as in the prior art explained above, by obtaining outputcurrents I₁ and I₂ as sums of collector currents with offsets. In thisembodiment, however, offsets are produced, not by the difference of theemitter areas of transistors as in the prior art, but by the constantoffset voltage applied by the constant voltage sources E₁ and E₂.Therefore, transistors Q₁, Q₂, Q₃ and Q₄ of the emitter-coupled pairs 10and 20 do not need to have a large emitter area ratio. In fact, they canbe of minimum the size available. Consequently, improved linearity canbe achieved in this embodiment while maintaining a high S/N ratio, agood high-frequency characteristic, a high direct current gain, and ahigh-speed operation capability, by incorporating appropriateconfigurations.

Such configurations will now be explained in the following, where thoseparts identical to those in the first embodiment will be given the samesymbols in the figures, and the explanations of these will be omitted.

Referring now to FIG. 6, there is shown a second embodiment of a lineardifferential amplifier according to the present invention. In thisembodiment, the constant voltage sources, E₁ and E₂ in the lastembodiment, are comprised of pairs of emitter-followers 21 and 22, and23 and 24. Each pair is comprised of emitter-followers includingtransistors with an emitter area ratio of 1:4, and each emitter-followeris connected to an emitter current source for a transistor. Namely, theconstant voltage source for the transistors Q₁ and Q₃ is comprised ofthe emitter-followers 21 and 22 where the emitter-follower 22 has atransistor Q₆ with an emitter area four times larger than that of atransistor Q₅ of the emitter-follower 21, and the emitter-followers 21and 22 are connected to emitter current sources 25a and 25b,respectively, which supply emitter currents I_(o) to the transistors Q₅and Q₆, respectively. Likewise, the constant voltage source for thetransistors Q₂ and Q₄ is comprised of the emitter-followers 23 and 24where the emitter-follower 24 has a transistor Q₈ with an emitter areafour times larger than that of a transistor Q₇ of the emitter-follower23, and the emitter-followers 23 and 24 are connected to emitter currentsources 25c and 25d, respectively, which supply emitter currents I_(o)to the transistors Q₇ and Q₈, respectively.

In this embodiment, due to the difference in emitter areas of pairsemitter-followers, the base-emitter voltages V_(be) for the transistorsQ₅ and Q₆ are given by:

    V.sub.be (Q.sub.5)=V.sub.t 1n(I.sub.c /I.sub.s)(V)

    V.sub.be (Q.sub.6)=V.sub.t 1n(I.sub.c /4I.sub.s)(V)

where I₅ is the saturation current of the transistors, I_(c) is thecollector current of the transistors, and V_(t) is the thermal voltageof the transistors. Thus, there is a constant voltage gap of V_(t)1n4(V) between the transistors Q₅ and Q₆, and this produces the offsetsfor the collector currents of the transistors Q₁ and Q₃. Similarly, thesame constant voltage gap with the opposing sign exists between thetransistors Q₇ and Q₈, and this produces the offsets for the collectorcurrents of the transistors Q₂ and Q₄.

The improved linearity is achieved in this embodiment, just as in thelast embodiment, by obtaining output currents I₁ and I₂ as sums of thecollector currents with offsets. In addition, by the use of theemitter-followers it is possible in this embodiment to achieve improvedlinearity while maintaining a high S/N ratio, a good high-frequencycharacteristic, a high direct current gain, and a high-speed operationcapability. This is because, as in the last embodiment, the transistorsQ₁, Q₂, Q₃ and Q₄ do not need to have a larger emitter area ratio, andcan be of minimum size.

Referring now to FIG. 7, there is shown a third embodiment of a lineardifferential amplifier according to the present invention. In thisembodiment, the constant voltage sources in the embodiment of FIG. 6 aremodified such that the transistors of paired emitter-followers Q₅ andQ₉, Q₇ and Q₁₀ now have the same emitter areas, but at the same time thetransistors Q₅ and Q₇ are connected to the emitter current sources 30aand 30b, respectively, which supply emitter currents 4I_(o) which isfour times greater than that supplied by the emitter current sources 25band 25d to the transistors Q₉ and Q₁₀.

It is obvious that by this configuration, there is a constant voltagegap of V_(t) 1n4(V) between the transistors Q₅ and Q₉ and -V_(t) 1n4(V)between the transistors Q₇ and Q₁₀, just as in the embodiment of FIG. 6.Thus, all the advantages of the embodiment of FIG. 6 can be obtained bythis embodiment as well.

Referring now to FIG. 8, there is shown a fourth embodiment of a lineardifferential amplifier according to the present invention. In thisembodiment, the constant voltage sources in the embodiment of FIG. 6 aremodified such that each pair transistors of paired emitter-followers Q₉and Q₁₃, and Q₁₀ and Q₁₄ now have an emitter area ratio of 1:2, but atthe same time transistors of the emitter-coupled pairs, Q₁ and Q₄ in theembodiment of FIG. 6, are also replaced by transistors Q₁₁ and Q₁₂ whichhave the emitter area twice as large as that of the transistors Q₂ andQ₃.

It is clear that by this configuration, the same offsets as in theembodiment of FIG. 6 are produced for collector currents of thetransistors Q₂, Q₃, Q₁₁ and Q₁₂. Also, the effect of combiningtransistors of different emitter areas and emitter-followers can stillbe a tolerable level because the emitter area ratio involved here isonly 1:2. Thus, practically all the advantages of the embodiment of FIG.6 may be obtained by this embodiment.

Referring now to FIG. 9, there is shown a fifth embodiment of a lineardifferential amplifier according to the present invention. In thisembodiment, the features of the third embodiment of FIG. 7 and thefourth embodiment of FIG. 8 are combined by replacing the transistors Q₉and Q₁₀ in FIG. 7 with transistors Q₂₅ and Q₂₆ such that each pairtransistors of paired emitter-followers Q₅ and Q₂₅, and Q₇ and Q₂₆ nowhave an emitter area ratio of 1:2, and at the same time connecting thetransistors Q₅ and Q₇ to the emitter current sources 47a and 47b,respectively, which supply emitter currents 2I_(o) which is twicegreater than that supplied by the emitter current sources 25b and 25d tothe transistors Q₂₅ and Q₂₆. Again, practically all the advantages ofthe embodiment of FIG. 6 may be obtained by this embodiment.

Referring now to FIG. 10, there is shown a sixth embodiment of a lineardifferential amplifier according to the present invention. In thisembodiment, each of the constant current sources, 7 and 8 in theembodiment of FIG. 6, and the emitter current sources, 25a, 25b and 25cand 25d in the embodiment of FIG. 6 comprise a transistor with aresistor connected between its emitter and ground. Namely, the constantcurrent source for the transistors Q₁ and Q₂ comprises a transistor Q₁₅with a resistor 33a connected between its emitter and ground, theconstant current source for the transistors Q₃ and Q₄ comprises atransistor Q₁₆ with a resistor 33b connected between its emitter andground, where these transistors Q₁₅ and Q₁₆ are biased by the constantvoltage 34.

Likewise, the emitter current source for the transistor Q₅ comprises atransistor Q₁₇ with a resistor 35a connected between its emitter andground, the emitter current source for the transistor Q₆ comprises atransistor Q₁₈ with a resistor 35b connected between its emitter and theground, the emitter current source for the transistor Q₇ is comprised ofa transistor Q₁₉ with a resistor 35c connected between its emitter andground, the emitter current source for the transistor Q₈ comprises atransistor Q₂₀ with a resistor 35d connected between its emitter andground, where these transistors Q₁₇, Q₁₈, Q₁₉ and Q₂₀ are biased by theconstant voltage 36.

Due to this configuration of various current sources, the noise producedby these current sources is reduced in this embodiment while retainingall the advantage of the embodiment of FIG. 6, so that in thisembodiment an even higher S/N ratio may be obtained.

It is obvious that similar improvement of an S/N of FIG. 8 byimplementing the similar configurations as done in this embodiment forthe embodiment of FIG. 6.

Referring now to FIG. 11, there is shown a seventh embodiment of alinear differential amplifier according to the present invention. Inthis embodiment, the linear differential amplifier of FIG. 5 is modifiedby connecting diodes D₁, D₂, D₃ and D₄ between the emitter of each ofthe transistors Q₁, Q₂, Q₃ and Q₄ and the constant current sources 7 and8, where the diodes D₁, D₂, D₃ and D₄ are all equivalent to each other.

By means of these additional diodes, it is possible in this embodimentto obtain an even wider range of linearity while retaining all theadvantages of the embodiment of FIG. 5.

Referring now to FIG. 12, where is shown an eighth embodiment of alinear differential amplifier according to the present invention. Inthis embodiment, the linear differential amplifier of FIG. 11 is furthermodified by replacing the diodes D₁, D₂, D₃ and D₄ with transistors Q₂₇,Q₂₈, Q₂₉, and Q₃₀, respectively, where each of these transistors Q₂₇,Q₂₈, Q₂₉, and Q₃₀ has its base and collector connected together so as tofunction effectively as a diode. Thus, as in the seventh embodimentabove, it is also possible in this embodiment to obtain an even widerrange of linearity while retaining all the advantages of the embodimentof FIG. 5.

There are several other configurations based on the various embodimentsdescribed so far, each one of which can possesses the various advantagesof the various embodiments described above together in one. Suchconfigurations will now be described.

Referring now to FIG. 13, there is shown a ninth embodiment of a lineardifferential amplifier according to the present invention. In thisembodiment, the linear differential amplifier of FIG. 11 is equippedwith pairs of emitter-followers 21 and 37, and 23 and 38, similar tothose described above in the second embodiment of FIG. 6, as theconstant voltage sources. Here, the constant voltage sources in theembodiment of FIG. 6 are modified such that each pair transistors ofpaired emitter-followers Q₅ and Q₂₁, and Q₇ and Q₂₂ now have an emitterarea ratio of 1:16.

Referring now to FIG. 14, there is shown a tenth embodiment of a lineardifferential amplifier according to the present invention. In thisembodiment, the linear differential amplifier of FIG. 11 is equippedwith pairs of emitter-followers 22 and 26, and 24 and 28, where theemitter-followers 22 and 24 appeared in the second embodiment of FIG. 6while the emitter-followers 26 and 28 appeared in the third embodimentof FIG. 7, as the constant voltage sources.

Referring now to FIG. 15, there is shown an eleventh embodiment of alinear differential amplifier according to the present invention. Inthis embodiment, the linear differential amplifier of FIG. 11 ismodified by replacing the transistors Q₁ and Q₄ by the transistors Q₁₁and Q₁₂ which have the emitter area twice as large as those of thetransistors Q₂ and Q₃ and which appeared in the fourth embodiment ofFIG. 8, and also by replacing the diodes D₁ and D₃ connected to thetransistors Q₁₁ and Q₁₂ by diodes D₅ and D₆, each of which is equivalentto two diodes D₁ and D₄ connected in series. In addition, thisdifferential amplifier is equipped with pairs of emitter-followers 27and 39, and 29 and 40, where each pair transistors of pairedemitter-followers Q₉ and Q₂₃, and Q₁₀ and Q₂₄ have an emitter area ratioof 1:4, as the constant voltage sources.

Referring now to FIG. 16, there is shown a twelfth embodiment of alinear differential amplifier according to the present invention. Inthis embodiment, the linear differential amplifier of FIG. 15 is furthermodified by changing the pairs of emitter-followers 27 and 39, and 29and 40 to pairs of emitter-followers 21 and 41, and 23 and 42, such thatthe transistors of paired emitter-followers Q₅ and Q₉, Q₇ and Q₁₀ nowhave the same emitter areas, but at the same time the transistors Q₉ andQ₁₀ are connected to the emitter current sources 30a and 30b,respectively, which supply emitter currents 4I_(o) which is four timesgreater than that supplied by the emitter current sources 25a and 25c tothe transistors Q₅ and Q₇.

Referring now to FIG. 17, there is shown a thirteenth embodiment of alinear differential amplifier according to the present invention. Inthis embodiment, the linear differential amplifier of FIG. 13 is furthermodified by changing the pairs of emitter-followers 21 and 37, and 23and 38 to the pairs of emitter-followers 21 and 22, and 23 and 24, suchthat the transistors of the paired emitter-followers Q₅ and Q₆, Q₇ andQ₈ have an emitter area ratio of 1:4. In addition, in this embodiment,diodes D₇, D₈, D₉, and D₁₀ are connected between the emitter of each ofthe transistors Q₅, Q₇, Q₆, and Q₈, respectively, and the constantcurrent sources 25a, 25b, 25c, and 25d, respectively, of which each ofthe diodes D₇ and D₈ is equivalent to the diodes D₁ while each of thediodes D₉ and D₁₀ is equivalent to four diodes D₁, D₂, D₃, and D₄connected together in series. The use of these diodes D₇, D₈, D₉, andD₁₀ connected to the transistors Q₅, Q₇, Q₆, and Q₈ of the pairs of theemitter-followers 21 and 22, and 23 and 24 make it possible to improvethe linearity without employing transistors of larger emitter areas.

Referring now to FIG. 18, there is shown a fourteenth embodiment of alinear differential amplifier according to the present invention. Inthis embodiment, the linear differential amplifier of FIG. 17 is furthermodified by changing the pairs of emitter-followers 21 and 22, and 23and 24 to the pairs of emitter-followers 43 and 45, and 44 and 46, suchthat the transistors of the paired emitter-followers Q₅ and Q₂₅, Q₇ andQ₂₆ have an emitter area ratio of 1:2, and at the same time byconnecting the transistors Q₅ and Q₇ to the emitter current sources 47aand 47b, respectively, which supply emitter currents 2I_(o) which isfour times greater than that supplied by the emitter current sources 25band 25d to the transistors Q₂₅ and Q₂₆, and also by replacing the diodesD₉, and D₁₀ by diodes D₁₁ and D₁₂, each of which is equivalent to twodiodes D₁ and D₄ connected together in series,. Again, the use of thesediodes D₇, D₈, D₁₁, and D₁₂ connected to the transistors Q₅, Q₇, Q₂₅,and Q₂₆ of the pairs of the emitter-followers 43 and 45, and 44 and 46make it possible to improve the linearity without employing transistorsof larger emitter areas.

Referring now to FIG. 19, there is shown a fifteenth embodiment of alinear differential amplifier according to the present invention. Inthis embodiment, the linear differential amplifier of FIG. 15 is furthermodified by changing the pairs of emitter-followers 27 and 39, and 29and 40 to the pairs of emitter-followers 27 and 31, and 29 and 32, suchthat the transistors of the paired emitter-followers Q₉ and Q₁₃, Q₁₀ andQ₁₄ have an emitter area ratio of 1:2. In addition, in this embodiment,diodes D₁₃, D₁₄, D₁₅, and D₁₆ are connected between the emitter of eachof the transistors Q₉, Q₁₀, Q₁₃, and Q₁₄, respectively, and the constantcurrent sources 25a, 25b, 25c, and 25d, respectively, of which each ofthe diodes D₁₅ and D₁₆ is equivalent to the diode D₁ while each of thediodes D₁₃ and D₁₄ is equivalent to two diodes D₁ and D₄ connectedtogether in series. Again, the use of these diodes D₁₃, D₁₄, D₁₅, andD₁₆ connected to the transistors Q₉, Q₁₀, Q₁₃, and Q₁₄ of the pairs ofthe emitter-followers 27 and 31, and 29 and 32 make it possible toimprove the linearity without employing transistors of larger emitterareas.

Referring now to FIG. 20, there is shown a sixteenth embodiment of alinear differential amplifier according to the present invention. Inthis embodiment, the linear differential amplifier of FIG. 19 is furthermodified by changing the emitter-followers 31 and 32 toemitter-followers 48 and 49, such that the transistors of the pairedemitter-followers Q₅ and Q₉, Q₇ and Q₁₀ have the same emitter areas, andat the same time by connecting the transistors Q₉ and Q₁₀ to the emittercurrent sources 47a and 47b, respectively, which supply emitter currents2I_(o) which is four times greater than that supplied by the emittercurrent sources 25a and 25c to the transistors Q₅ and Q₇, and also byreplacing the diodes D₁₃ and D₁₄ by diodes D₇ and D₈, each of which isequivalent to the diodes D₁. Again, the use of these diodes D₇, D₈, D₁₅,and D₁₆ connected to the transistors Q₅, Q₇, Q₂₅, and Q₂₆ of the pairsof the emitter-followers 21 and 48, and 23 and 49 make it possible toimprove the linearity without employing transistors of larger emitterareas.

It is to be noted that in the ninth to sixteenth embodiments of FIGS.13-20, any one of the diodes may be replaced by a transistor with itsbase connected to its collector, just as in the eighth embodiment ofFIG. 12 with respect to the seventh embodiment of FIG. 11.

It should readily be understood that the specific ratio such as 1:4 or1:2 has been used in the preceding descriptions for the sake ofdefiniteness, but they only need to be followed approximately, andpractically the same advantages can be obtained with such approximation.

It can also be seen that a linear differential amplifier of the presentinvention can be utilized not only in an electric filter, but anywherewhere the improved linearity of an amplifier is desirable such as, forexample, an initial stage for an amplifier of the operational amplifiertype.

Furthermore, many modifications and variations of the embodimentsexplained may be made without departing from the novel and advantageousfeatures of this invention. Accordingly, all such modifications andvariations are intended to be included within the scope of the appendedclaims.

What is claimed is:
 1. A linear differential amplifier, comprising:apair of first and second transistors with their emitters coupled to eachother; a pair of third and fourth transistors with their emitterscoupled to each other, a collector of said first transistor beingconnected to a collector of said third transistor and a collector ofsaid second transistor being connected to a collector of said fourthtransistor; a pair of input terminals, one of which being coupled to abase of said first transistor, the other one of which being coupled to abase of said fourth transistor; a pair of output terminals, one of whichbeing connected to said collectors of said first and said thirdtransistor, the other one of which being connected to said collectors ofsaid second and said fourth transistors; first voltage source means forapplying first offset DC voltage between one of said input terminals anda base of said third transistor, said first voltage source meansincluding a first pair of emitter-followers with each of saidemitter-follower including transistors of same emitter areas butdifferent collector currents, and first emitter current sources for eachtransistor of said first pair of emitter-followers which supply emittercurrents corresponding to the collector currents; second voltage sourcemeans for applying second offset DC voltage of the same magnitude assaid first offset DC voltage, between one of said input terminals and abase of said second transistor, said second voltage source meansincluding a second pair of emitter-followers with each saidemitter-follower including transistors of same emitter areas butdifferent collector currents, and second emitter current sources foreach transistor of said second pair of emitter-followers which supplyemitter currents corresponding to the collector currents; constantcurrent source means for supplying emitter currents to said first,second, third, and fourth transistors; and load resistor means forconverting collector currents of said first, second, third, and fourthtransistors into output voltages.
 2. A linear differential amplifier,comprising:a pair of first and second transistors with their emitterscoupled to each other; a pair of third and fourth transistors with theiremitters coupled to each other, a collector of said first transistorbeing connected to a collector of said third transistor and a collectorof said second transistor being connected to a collector of said fourthtransistor, and said first and fourth transistors having emitter areasdifferent from those of said second and third transistors; a pair ofinput terminals, one of which being coupled to a base of said firsttransistor, the other one of which being coupled to a base of saidfourth transistor; a pair of output terminals, one of which beingconnected to said collectors of said first and said third transistor,the other one of which being connected to said collectors of said secondand said fourth transistors; first voltage source means for applyingfirst offset DC voltage between one of said input terminals and a baseof said third transistor, said first voltage source means including afirst pair of emitter-followers with each said emitter-followerincluding transistors of different emitter areas, and first emittercurrent sources for supplying constant emitter currents to saidtransistors of said first pair of emitter-followers; second voltagesource means for applying second offset DC voltage of the same magnitudeas said first offset DC voltage, between one of said input terminals anda base of said second transistor, said second voltage source meansincluding a second pair of emitter-followers with each saidemitter-follower including transistors of different emitter areas, andsecond emitter current sources for supplying constant emitter currentsto said transistors of said second pair of emitter-followers; constantcurrent source means for supplying emitter currents to said first,second, third, and fourth transistors; and load resistor means forconverting collector currents of said first, second, third, and fourthtransistors into output voltages.
 3. A linear differential amplifier,comprising:a pair of first and second transistors with their emitterscoupled to each other; a pair of third and fourth transistors with theiremitters coupled to each other, a collector of said first transistorbeing connected to a collector of said third transistor and a collectorof said second transistor being connected to a collector of said fourthtransistor, and said first and fourth transistors having emitter areasdifferent from those of said second and third transistors; a pair ofinput terminals, one of which being coupled to a base of said firsttransistor, the other one of which being coupled to a base of saidfourth transistor; a pair of output terminals, one of which beingconnected to said collectors of said first and third transistor, theother one of which being connected to said collectors of said second andsaid fourth transistors; first voltage source means for applying firstoffset DC voltage between one of said input terminals and a base of saidthird transistor, said first voltage source means including a first pairof emitter-followers with each said emitter-follower includingtransistors of same emitter areas but different collector currents, andfirst emitter current sources for each transistor of said first pair ofemitter-followers which supply emitter currents corresponding to thecollector currents; second voltage source means for applying secondoffset DC voltage of the same magnitude as said first offset DC voltage,between one of said input terminals and a base of said secondtransistor, said second voltage source means including a second pair ofemitter-followers with each said emitter-follower including transistorsof same emitter areas but different collector currents, and secondemitter current sources for each transistor of said second pair ofemitter-followers which supply emitter currents corresponding to thecollector currents; constant current source means for supplying emittercurrents to said first, second, third, and fourth transistors; and loadresistor means for converting collector currents of said first, second,third, and fourth transistors into output voltages.
 4. A lineardifferential amplifier, comprising:a pair of first and secondtransistors with their emitters coupled to each other, each of whichhaving a diode connected to its emitter; a pair of third and fourthtransistors with their emitters coupled to each other, each of whichhaving a diode connected to its emitter, a collector of said .[.frist.]..Iadd.first .Iaddend.transistor being connected to a collector of saidthird transistor and a collector of said second transistor beingconnected to a collector of said fourth transistor; .Iadd.a pair ofinput terminals; .Iaddend. a pair of output terminals, one of whichbeing connected to said collectors of said first and said third.[.transistor.]. .Iadd.transistors.Iaddend., the other one of whichbeing connected to said collectors of said second and said fourthtransistors; a first voltage source means for applying first offset DCvoltage between one of said input terminals and a base of said thirdtransistor, said first voltage source means including a first pair ofemitter-followers with each said emitter-follower including transistorsof different emitter areas, and first emitter current sources forsupplying constant emitter currents to said transistors of said firstpair of emitter-followers; a second voltage source means for applying asecond offset DC voltage of the same magnitude as said first offset DCvoltage, between the other one of said input terminals and a base ofsaid second transistors, said second voltage source means including asecond pair of emitter-followers with each of said emitter-followersincluding transistors of different emitter areas, and second emittercurrent sources for supplying constant emitter currents to thetransistors of said second pair of emitter-followers; constant currentsource means for supplying emitter currents to said first, second,third, and fourth transistors; and load resistor means for convertingcollector currents of said first, second, third, and fourth transistorsinto output voltages.
 5. The amplifier of claim 4, wherein one of thetransistors of the first pair of emitter-followers has a number ofdiodes connected to its emitter while another one of the transistors ofthe first pair of emitter-followers has a different number of diodesconnected to its emitter, and wherein one of the transistors of thesecond pair of emitter-followers has a number of diodes connected to itsemitter while another one of the transistors of the second pair ofemitter-followers has a different number of diodes connected to itsemitter.
 6. A linear differential amplifier, comprising:a pair of firstand second transistors with their emitters coupled to each other, eachof which having a diode connected to its emitter; a pair of third andfourth transistors with their emitters coupled to each other, each ofwhich .[.have.]. .Iadd.having .Iaddend.a diode connected to its emitter,a collector of said .[.third.]. .Iadd.first .Iaddend.transistor beingconnected to a collector of said third transistor and a collector ofsaid second transistor being connected to a collector of said fourthtransistor; .Iadd.a pair of input terminals; .Iaddend. a pair of outputterminals, one of which being connected to said collectors of said firstand said third transistor, the other one of which being connected tosaid collectors of said second and said fourth transistors; a firstvoltage source means for applying first offset DC voltage between one ofsaid input terminals and a base of said third transistor, said firstvoltage source means including a first pair of emitter-followers witheach said emitter-follower including transistors of different emitterareas and different collector currents, and emitter current sources foreach transistor of the emitter-followers which supply emitter currentscorresponding to the collector currents; a second voltage source meansfor applying .Iadd.a .Iaddend.second offset DC voltage of the samemagnitude as said first offset DC voltage, between the other one of saidinput terminals and a base of said second transistor, said secondvoltage source means including a second pair of emitter-followers.[.followers.]. with each of said emitter-followers includingtransistors of different emitter areas and different collector currents,and emitter current sources for each transistor of the emitter-followerswhich supply emitter currents corresponding to the collector currents;constant current source means for supplying emitter currents to saidfirst, second, third, and fourth transistors; and load resistor meansfor converting collector currents of said first, second, third, andfourth transistors into output voltages.
 7. The amplifier of claim 6,wherein one of the transistors of the first pair of emitter-followershas a number of diodes connected to its emitter while another one of thetransistors of the first pair of emitter-followers has a differentnumber of diodes connected to its emitter, and wherein one of thetransistors of the second pair of emitter-followers has a number ofdiodes connected to its emitter while another one of the transistors ofthe second pair of emitter-followers has a different number of diodesconnected to its emitter.
 8. A linear differential amplifier,comprising:a pair of first and second transistors with their emitterscoupled to each other, one of which having a number of diodes connectedto its emitter while another one of which having a different number ofdiodes connected to its emitter; a pair of third and fourth transistorswith their emitters coupled to each other, one of which having a numberof diodes connected to its emitter while another one of which having adifferent number of diodes connected to its emitter, a collector of saidfirst transistor being connected to a collector of said third transistorand a collector of said second transistor being connected to a collectorof said fourth transistor, and said first and fourth transistors havingemitter areas different from that of said second and third transistors;a pair of input terminals, one of which being coupled to the base ofsaid first transistor, the other one of which being coupled to the baseof said fourth transistor; a pair of output terminals, one of whichbeing connected to the collectors of said first and said thirdtransistors, the other one of which being connected to said collectorsof said second and said fourth transistors; first voltage source meansfor applying first offset DC voltage between one of said input terminalsand a base of said third transistor, said first voltage source meansincluding a first pair of emitter-followers with each of saidemitter-followers including transistors of different emitter areas, andfirst emitter current sources for supplying constant emitter currents tosaid transistors of said first pair of emitter-followers; second voltagesource means for applying second offset DC voltage of the same magnitudeas said first offset DC voltage, between the other one of said inputterminals and a base of said second transistor, said second voltagesource means including a second pair of emitter-followers with each ofsaid emitter-followers including transistors of different emitter areas,and second emitter current sources for supplying constant emittercurrents to the transistors of said second pair of emitter-followers;constant current source means for supplying emitter currents to saidfirst, second, third, and fourth transistors; and load resistor meansfor converting collector currents of said first, second, third, andfourth transistors into output voltages.
 9. The amplifier of claim 8,wherein one of the transistors of the first pair of emitter-followershas a number of diodes connected to its emitter while another one of thetransistors of the first pair of emitter-followers has a differentnumber of diodes connected to its emitter, and wherein one of thetransistors of the second pair of emitter-followers has a number ofdiodes connected to its emitter while another one of the transistors ofthe second pair of emitter-followers has a different number of diodesconnected to its emitter.
 10. A linear differential amplifier,comprising:a pair of first and second transistors with their emitterscoupled to each other, one of which having a number of diodes connectedto its emitter while another one of which having a different number ofdiodes connected to its emitter; a pair of third and fourth transistorswith their emitters coupled to each other, one of which having a numberof diodes connected to its emitter while another one of which having adifferent number of diodes connected to its emitter, a collector of saidfirst transistor being connected to a collector of said third transistorand a collector of said second transistor being connected to a collectorof said fourth transistor, and said first and said fourth transistorshaving emitter areas different from that of said second and said thirdtransistors; a pair of input terminals, one of which being coupled tothe base of said first transistor, the other one of which being coupledto the base of said fourth transistor; a pair of output terminals one ofwhich being connected to the collectors of said first and said thirdtransistors, the other one of which being connected to the collectors ofsaid second and said fourth transistors; first voltage source means forapplying first offset DC voltage between one of said input terminals andthe base of said third transistor, said first voltage source meansincluding a first pair of emitter-followers with each of saidemitter-followers including transistors of the same emitter areas butdifferent collector currents, and first emitter current sources for eachtransistor of said first pair of emitter-followers which supply emittercurrents corresponding to the collector currents; second voltage sourcemeans for applying second offset DC voltage of the same magnitude assaid first offset DC voltage, between the other one of said inputterminals and the base of said second transistor, said second voltagesource means including a second pair of emitter-followers with each saidemitter-followers including transistors of the same emitter areas butdifferent collector currents, and second pair of emitter-followers whichsupply emitter currents corresponding to the collector currents;constant current source means for supplying emitter currents to saidfirst, second, third, and fourth transistors, and load resistor meansfor converting collector currents of said first, second, third, andfourth transistors into output voltages.
 11. The amplifier of claim 10,wherein each of the transistors of the first pair of emitter-followershas a diode connected to its emitter, and wherein each of thetransistors of the second pair of emitter-followers has a diodeconnected to its emitter.